Shaun Spiers, Chief Executive of CPRE, said Mr Boles, the founder of the Policy Exchange think-tank, was not in charge of the detail of his new brief.

“Nick Boles does not appear to know how much of England is really built on,” he said. “Nor does he seem to understand that the countryside does not always have to be outstandingly beautiful to be worth protecting.

“It is equally crucial that people have places to enjoy peace and tranquillity.

“When he was running a think tank, Nick Boles specialised in interesting if somewhat unrealistic ideas. He is no longer an intellectual gadfly. He is a minister with a serious job and it is time that he got serious.”

The CPRE said Mr Boles was wrong to argue that that only 9 per cent of England was built on and that this should rise by one third to 12 per cent to meet housing demand. The group claimed that the government’s own figures showed 12% of England’s land area was already developed and that this was higher than most countries in Europe.

Ben Cowell, from the National Trust, accused Mr Boles of making “back of the fag packet” calculations.

“He’s talking here about increasing by a third the amount of developed land. Three per cent of the country is an area about the size of Cornwall and we don’t think that you need to build on green-field to quite this extent,” he told BBC Radio 4’s Today programme.

“You can build, actually, by using previously developed land, you can bring empty homes back into use, you can make urban areas more dense.”

Mr Cowell acknowledged there was a need for development but stressed it needed to be done carefully.